Digital audio evolves back to the single bit element DAC

Back in the late 80s I remember when Digital audio DACs were just industrial DACs that did not pass the DC specification tests. One bit DACs were usually fairly noisy, but Cirrus Logic designers took care of that problem (See their solution a little further down in this blog).

Just to show you some of the older designs, back in 1985, Ira Miller wrote a paper1 regarding A custom six-bit DAC, a three-channel multiplexer, a four-channel amplifier, and a comparator for Personal Computers as the interface to a cassette recorder and the audio sound channel. It also interfaced joysticks to the PC.

The schematic of the IC in Reference 1 (Image courtesy of Reference 1)

Well we have certainly come a long way from that effort 30 years ago (When Cirrus Logic began) to the tiny, low-power, Hi-Fi DACs that fit into headphones in the mobile audio market.

Better content is driving the need for better hardware. We have progressed from the CD to MP3 and now to:

Similar to MP3, Free Lossless Audio Codec (FLAC) is virtually lossless in that it compresses the audio with no loss of fidelity, just as Zip works on files, but with far more advanced compression that is audio-specific.

Cirrus Logic’s CS43130 is their most recent MasterHIFI DAC and Amplifier for this effort.

Here is where the Cirrus Logic designers improved the 1-bit DAC, they crafted 512 single-cell DACs into this architecture which reduces jitter degradation of good audio sound. The IC also filters out unwanted noise through each of the 512 DACs in sequence. In the earliest days of the compact disc, DACs did not employ oversampling, and thus most of the image energy removal was done with a high order analog circuit.

With up to -108 dB of THD+N and 130 dB of Dynamic Range distortion cannot be heard and audio from the lowest levels to the loudest will not have reduced quality of sound.

The IC’s amplifier is able to drive large, over-the-ear high-impedance headphones, with no problem---while helping to extend the phone’s battery. These large headphones are becoming very popular and users are becoming aware of audible benefits of having large headphone drivers. What makes these types of headphones complicated is that they have higher impedances up to 600 Ohms, as compared to 16 or 32 Ohms for in-ear headphones. This means they require a higher voltage to be driven correctly, without distortion.

In a typical mobile headphone, the amplifier output delivers up to 1Vrms, which is fine for smaller impedances, but a 1Vrms driven into large impedance headphones means the volume can be too low for comfortable listening levels or the fine detail getting lost when listening to low level audio such as in classical music.

The CS43130 can drive up to 1.7Vrms at 600 Ohms, which delivers the correct output levels for the larger over the ear headphones and maintain the level of detail that gives the listener a better audio experience.

The impedance of the headphones is automatically detected upon plug in, the correct voltage level is then automatically set to ensure safe and correct levels for the headphones being used.

I really like the design architecture and the technical detail to which Cirrus Logic designers paid attention in this IC.

Not so far away in time, the most important measure taken into account when delivering multimedia content, images, video or audio, to a human end-point listener was how this content was perceived, the quality in terms of perception. That still applies to voice transmission over telephone "lines" and video content broadcasting in digital television.

For that and other reasons MP3 and other compression formats have been so sucessful, but at the cost of lossing data.

"Similar to MP3, Free Lossless Audio Codec (FLAC) is virtually lossless", FLAC is similar to MP3 as it serves for compressing audio, they also work as audio data containers, but the 100% reproduction fidelity (input and output streams are bit-to-bit identical) which is achievable by FLAC can not be obtained from MP3.

MP3HD, from Technicolor, on the contrary, does allow to obtain a lossless compression-decompression process while maintaining compatibility with MP3. But this second feature is, to my opinion, a fake. This format simply incorporates two data streams in the same file, one stream is compressed using the standard MP3 format and the other using the lossless format.

Former colleagues from the CEETI, where I was a researcher at the UCLV, were working on high compression ratio encoders/decoders for EEG, audio and EEG signals. They were able to abtain 1/40 compression ratio using vectorial quantization combined with several bit encoding techniques. Of course it was lossy, but at first it was destined to be stored for later observations by humans.

Steve, where's the detail on the CS43130? "512 single-cell DACs" sounds like an interesting approach but there's no clue about how it actually works.

I tried finding some information on the web but what I found was that "512 single-cell DACs" is simply a bit of investor bait. Cirrus has a product page but it has no detail either. The datasheet is "available by request".

Steve, with your position in the industy you should be able to get some real news on this part.

@MrAnalog--I am asking Cirrus to address your interest in CS43130 architecture. Unfortunately, I cannot change the policy of a supplier. You may have to request a datasheet as they suggest, but I have contacted Cirrus and asked them to address your interest.

But I am sure that if you directly contact them as an interested designer that they would help you.

Thanks for your interest in the CS43130 hi-fi DAC. It's always good to see discussion taking place! As you noted, the data sheet for this product is by request on our website, and we do that primarily because of competitive reasons. It's a support request form that gets channeled to a sales rep for follow up. Regarding the 512 single-cell DAC elements that form the DAC architecture of the CS43130, they're designed in a sequential method so that each element uses a clean clock source as it's reference and doesn't inherit jitter from the previous element, so that by the end of the 512 element chain, the audio signal is clean. In addition the elements sequentially filter out the unwanted frequencies to stop them affecting the wanted audio frequencies. The hard task is designing the element architecture, plus hooking them up together in such a way as to make this work and at the same time, make sure the actual sound produced from the DAC is as good as possible. If you'd like to follow up with me at jonathan.taylor@cirrus.com I'd be glad to provide additional technical information and see what we can do to answer your questions.